Gas turbines with sequential combustion are known and have been proved to be successful in industrial use. Such a gas turbine, which has been known among experts as GT24/26, follows for example from an article by Joos, F. et al., “Field Experience of the Sequential Combustion System for the ABB GT24/GT26 Gas Turbine Family”, IGTI/ASME 98-GT-220, 1998 Stockholm. In this document, FIG. 1 shows a basic construction of such a gas turbine, and FIG. 1 is reproduced in the present disclosure as FIG. 1. Furthermore, such a gas turbine follows from EP-B1-0 620 362.
The stator vanes 10 of the FIG. 1 gas turbine have a vane airfoil 11 which extends in the longitudinal direction and which is delimited in the flow direction of the hot gas (parallel arrows in FIG. 1) by a leading edge 14 and a trailing edge 15. In the longitudinal direction, the vane airfoil 11 is delimited by a vane tip 13 and an outer platform 12 (sometimes also referred to as a shroud, wherein this element in the following text is referred to as an outer platform). The vane tip 13 delimits the annular hot gas passage of the turbine on the inner side and can adjoin the rotor shaft of the turbine via a sealing segment. The outer platform 12, by its inner side 19, delimits the hot gas passage on the outside.
On the outer side of the outer platform 12, which is exposed to throughflow by a cooling medium (for example cooling air), a front and rear hook-like fastening element 16 or 17 are formed, which on the one hand serve for the fastening of the stator vane 10 on the inner casing of the turbine and on the other hand are made available for the locating and fixing of adjacent heat accumulation segments (“heat shields”. See FIG. 2, pos. 24) in the flow direction. For this purpose, on the rear fastening element 17 provision is made for a locating slot 18 into which a heat shield can be inserted. The locating slot 18 is delimited towards the outer platform 12 by a horizontal base surface 18′ which together with the inclined inner side 19 of this outer platform 12 forms a wedge-shaped section 19′ in the region of the trailing edge 15, which section is characterized by a large material volume.
The transition 21 between the trailing edge 15 of the stator vane 10 and the outer platform 12 represents a region which can affect the service life of the stator vane 10 since a high thermal stress, which results from a thermal-mechanical mismatch between outer platform 12 and vane airfoil 11, is established within it, wherein this can lead to a peak in the mechanical stress, which results from the stress of the vane airfoil 11 which is impinged upon by the hot gas flow, being superimposed. The large material volume, which is mentioned above, in the wedge-shaped section 19′ above the trailing edge 15 can lead to a significant increase of the thermal stresses in this region which can be important for the service life of the stator vane 10 and therefore lead to a reduction of the service life itself, bearing in mind the fact that modern gas turbines involve high temperatures in respect to operating fluids, which in many cases lie beyond the permissible material temperature of economically usable materials.